The invention relates to a thermoforming machine with a cutting press disposed or linked thereafter for the molding of thermoplastic synthetic resin sheet stock into articles and for punching these articles from the sheet length. For this purpose, the thermoforming machine comprises a forming station, a heating unit, and an intermittent feed arrangement for the stock material, while the cutting press comprises a vertically movable top platen with the cutting die, a rigid table, and a likewise intermittent material feed arrangement.
The combination of a thermoforming machine with a cutting press connected thereafter is utilized in the series production of articles wherein, however, the series do not include excessively large numbers of pieces, i.e., wherein a tool performing both forming and cutting operations would be too expensive. This combination is furthermore advantageous in articles formed from a very thin sheet. The forming tools are relatively inexpensive, and economical strip steel dies can be used as the cutting dies.
Although it is known to use a common material feed arrangement for both the cutting press and the thermoforming machine, and thus in effect permanently connect these two units together as a single unit (see for example British Pat. No. 1,277,226, issued June 7, 1972), it is preferable, for various reasons, if the cutting press is associated with the thermoforming machine as a separate unit, i.e., has its own material feed arrangement. For example, by providing the cutting press and thermoforming machine as separate units, it is readily possible to dismount the cutting press and associate same with another machine, if this is necessary for manufacturing reasons; thus, it may be necessary, depending on the article being formed, to connect for example, a belt saw, a simple cross cutter, or a guillotine after the thermoforming machine. Moreover, it is technically possible to operate the cutting press at a higher cycle rate than the thermoforming machine. This can be done if the forming tool molds simultaneously two or three article series or rows per cycle (multiple mold). In this case, a single-row cutting die is sufficient for the cutting press, which die can sever the thus-formed band. Thereby this cutting die becomes especially inexpensive, and the cutting forces required are not as high as when the entire output must be cut all at once. The cutting press has its own feed or conveyor arrangement for this purpose, conventionally a wiper feed or conveyor for the formed band or sheet.
In the thermoforming machine a spiked sprocket chain has proved to be advantageous for use as the conveying system for the film sheet. Two such chains, which run in respective guide rails, are provided and engage the respective longitudinal edge zones of the sheet. The conveying systems terminates behind the forming station, so that it is possible thereafter to connect any further required machinery, e.g., cutting press, saw, cross cutter, etc.
When linking a thermoforming machine with a separate conveying system of this type to the cutting press with its own wiper type conveyor system, problems are encountered in the case of very high articles, e.g., containers, in the case of articles formed of very thin sheet material, as well as in the case of articles wherein no knobs or protrusions which can be engaged by the wiper can be formed due to the contour of the articles and/or the position of the cutting edge. With very high articles, the wiper cannot be introduced in between the produced articles, since the lifting-off height is insufficient. In the case of articles of a very thin sheet, there is the danger that the wiper dents the sidewalls.
It has been known in these cases merely to push the formed film sheet through the cutting press by means of the conveyor unit of the thermoforming machine and to effect a pull at the waste screen on the opposite side of the cutting press. However, with this arrangement, a high misalignment during the cutting step must be tolerated.